Issue 68

H. Mostafa et alii, Frattura ed Integrità Strutturale, 68 (2024) 19-44; DOI: 10.3221/IGF-ESIS.68.02

used throughout the slab or in the punching shear region of the column head, and comparative tests on connections with bending steel bars were performed. The fibers reduce deformations, increase ultimate punching shear loads, and transform failures from brittle to ductile. Results demonstrated that 1% fiber volume decreases deflections by 30% and enhances ductility and energy absorption. Ospina et al. [2] performed experiments to explore the use of FRP reinforcement in concrete slabs, comparing its behavior with traditional steel reinforcement. Ospina et al. [2] test results indicated that FRP-reinforced slabs do not experience punching shear failure triggered by FRP rupture, even with lighter reinforcement. The proposed equations address the unique characteristics of FRP reinforcement, as existing standards may not directly apply due to variations in elastic stiffness. Mu and Meyer [3] investigated experimentally the effect of fiber-reinforced glass bars in concrete slabs exposed to a central patched load. Results indicated that fiber mesh is more effective in bending, while randomly distributed fibers are somewhat better at punching shear. The critical punching shear perimeter is unaffected by fiber type, form, and volume ratio. Crushed glass aggregate influences slab strength and failure mode, but concerns about long-term alkali-silica reactions have been addressed. Zhang et al. [4] compared the results of three specimens of one-way concrete slab reinforced with CFRP grid reinforcement in addition to a specimen reinforced with steel bars. Findings indicated that higher CFRP reinforcement ratios are needed for sufficient flexural stiffness, and the Tureyen–Frosch shear equation is proposed for predicting the ultimate moment in FRP-reinforced slabs. Dimitrios et al. [5] predicted analytically the ultimate strength of fiber-reinforced polymer (FRP)-reinforced structural elements like flat slabs and bridge decks. The analytical model, validated with experimental data for FRP-reinforced slabs, offers a reliable framework for punching shear strength analysis, emphasizing the importance of knowing FRP bonding characteristics. Esfahani et al. [6] investigated the punching shear strengthening of flat slabs using Carbon-Fiber-Reinforced-Polymer (CFRP) sheets. Results show significant enhancement, especially for high-strength concrete with low steel reinforcement, but under cyclic loading, the effect diminishes. Stuart et al. [7] explored FRP rebar for concrete reinforcement, particularly in slabs, evaluating performance based on ACI, CSA, and Eurocode standards. Findings revealed variations in code accuracy, emphasizing the need for additional research to enhance the safety of FRP-reinforced concrete design. Abdulrahman et al. [8] studied experimentally and numerically strengthened flat slab-to-column corner connections with and without openings using CFRP sheets. The findings indicated that strengthening increased punching shear capacity by 11% for slabs without openings and up to 23% for slabs with openings. Hemzah et al. [9], investigating the punching shear performance of ten slab specimens considering variations in shape, reinforcement types (steel or CFRP), ratios, and the impact of double-layer reinforcement, highlighted that factors such as compressive strength and column shape significantly influence punching shear strength. A proposed formula, considering reinforcement type, ratio, concrete strength, and double-layer effect, showed good agreement with experimental results and existing codes. Said et al. [10] conducted an experimental and numerical program for thirteen lightweight concrete flat slab specimens to improve the punching shear resistance by using different strengthening techniques. The most effective method, radial shear reinforcement with (d/2) spacing, significantly improves punching shear capacity (77% with steel bars, 61% with glass fiber rods, and 54% with high-strength bolts). Kim and Lee [11] investigated the structural behavior of reinforced concrete flat slabs shear reinforced with GFRP vertical grids. Results from experiments showed increased shear strength with more and closer shear reinforcement. GFRP changed failure modes from brittle punching to flexure. Comparison with design codes revealed underestimation, with BS 8110 showing reasonable accuracy, emphasizing the effectiveness of GFRP in resisting punching shear. Otherwise, few studies have been conducted on FRP with grating-shaped performance characteristics and its effectiveness as a punching shear resistance. Full-scale studies on a concrete slab bridge deck strengthened with pultruded glass fiber gratings were conducted by Bank et al. [12]. The results comply with AASHTO recommendations. The investigation shows that FRP gratings could be viable reinforcements, providing reasonable deflections and load capacities over three times the service load, with failure modes distinct from steel-reinforced slabs. Bank et al. [13] conducted experimental and analytical research to investigate the influence of pultruded FRP grating cages on reinforced concrete beams, comparing their performance to a steel-reinforced control beam. The results and failure modes are detailed, with a proposed analytical model predicting failure loads and deflection at failure. The study suggests the potential for using FRP grating cages for concrete reinforcement in construction. Biddah [14] investigated the use of pultruded GFRP grating sections as structural reinforcement for bridge decks in place of steel reinforcement of concrete slabs. The grating significantly increases capacity and flexural stiffness, showing potential as an economical alternative for bridge deck construction, offering high strength, easy installation, and preventing local buckling failure. Devender et al. [15] investigated experimentally the mechanical and chemical characteristics of GFRP grating. The composite grating, formed by resin and fiberglass, undergoes tests and is chosen over mild steel due to its durability, rust-free nature, and cost-effectiveness. Gattescoa et al. [16] discussed experimental bending tests on full-scale, molded FRP grating, exploring varied support conditions and the influence of FRP covers on stiffness and resistance. Rib collaboration enhances load capacity, while improving performance may lead to premature failure.

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